Analysis of AC AC Dynamic Voltage Restorer for Mitigation of Multiple Sag Condition Sudeepthi Jangam & Sm Rahman

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Analysis of AC-AC Dynamic Voltage Restorer for Mitigation of

Multiple Sag Condition

Sudeepthi Jangam

PG Scholar Department of EEE,

Amrita Sai Institute of Science And Technology, Paritala; Krishna (Dt); A.P, India.

Sm. Rahman

Associate Professor Department of EEE,

Amrita Sai Institute of Science And Technology, Paritala; Krishna (Dt); A.P, India.

Abstract:

In this paper, Dynamic Voltage Restorer using AC - AC converter has been proposed to mitigate the voltage sag/ swell and multiple sag. Dynamic Voltage Restorer (DVR) is an effective custom power devices used to protect the sensitive loads against voltage sag and swell. The single phase AC-AC converter has been employed to perform the direct AC/AC conversion. The AC voltage, which is a greater or less voltage than the line voltage. Hence it enhances the voltage restoration capability of DVR. The gating pulses for the bidirectional switch are generated using sinusoidal PWM technique and its associated circuitry. By connecting the matrix converter’s input terminals on the load side and injecting the compensation voltages on the supply-side, it is possible to hold a constant input voltage, resulting in an efficient solution for compensating deep voltage sags and swells. Different solutions have been developed to protect sensitive loads against such disturbances but the DVR is considered to be the most efficient and effective solution. Its appeal includes lower cost, smaller size and its dynamic response to the disturbance. This research described DVR principles and voltage restoration methods for balanced and/or unbalanced voltage sags and swells in a distribution system.

Index Terms– Dynamic Voltage Restorer (DVR), Single Phase Matrix Converter (SPMC).

I.INTRODUCTION

Power quality issues like voltage sag, voltage swell, transients and harmonics have become major concern

in most industries today, due to the increased application of sensitive loads [1]. These power quality problems can cause malfunctioning of sensitive equipments and process interruptions. Distribution system is mainly affected by voltage sag /swell power quality issue. Such voltage sag / swell have a major impact on the performance of the microprocessor-based loads as well as the sensitive loads [2]. Dynamic Voltage Restorer (DVR) is one of the most important custom power devices, which is connected in series with the distribution system to mitigate the power quality problems [3].It is connected in series between the supply and the critical load. The basic function of the DVR is to inject a controlled voltage into the system in order to regulate the load voltage.

The series compensation device DVR was introduced for voltage sag mitigation and has been adopted as a common solution to the problem.

Page 1164 dc-link passive elements some researchers have

focused their efforts to the topologies based on ac/ac power converters, which results in reduced maintenance requirements and improved power density [11-13]. DVR topologies with energy storage are highly favored to compensate deep level voltage sags in sensitive loads within a wide power factor range. However, this type of systems has significant drawbacks regarding complexity and overall cost (energy storage and power converter).

Fig.1. Principle of operation of the dynamic Voltage Restorer.

Among the existing DVR topologies with energy storage in ac form, various different types of switching power converters have been employed, being the matrix converter an attractive solution due to its operative advantages.

The advantages of these FACTS devices are their excellent in dynamic capability on mitigating disturbance. However these sag mitigation devices are based on inverter systems which consist of energy storage and power switches, this energy storage is well known for its short lifespan and its high cost.

II. DYNAMIC VOLTAGE RESTORER (DVR) Dynamic voltage restorer (DVR) is a power device connected in series to preserve the sensitive load when there is disturbance occurs at the point of common coupling (PCC). The typical DVR consisted of injection transformer connected in series with the distribution grid, a voltage sourced inverter connected

Page 1165 Fig. 2 the Block Diagram of Conventional DVR

Fig. 3 Conventional DVR

III. DEVELOPED TOPOLOGY

Based from the existing DVR topologies, the main parts of the DVR are the voltage source converter (VSC) and the controller method. This paper proposes a single phase matrix converter (SPMC) topology as a direct AC-AC converter to eliminate the dc link or energy storage used in a typical DVR system. DC link or energy storage is well known for its high cost and short lifespan. Since the DC link is the most expensive part and therefore many researches tried to eliminate the use of this energy storage element [12]. SPMC is used to replace the voltage source inverter since the SPMC is well known for its capabilities in producing different waveforms using different switching techniques.

Fig. 4 Proposed Block Diagram of DVR.

Fig. 5 Proposed Block Diagram of DVR

Fig. 6 Basic DVR topologies

By applying Kirchhoff’s voltage law, the system equation for Fig. 6 is obtained as follows:

Where VL (t) denote the nominal load voltage, VF (t) for the fault voltage, and VIfor the inject voltage. Assuming pure sinusoidal waveforms for VL (t), VF (t), and VI(t), the following equations can be written;

Page 1166 IV.DVR with Matrix Converter

Dynamic voltage restorer (DVR) is a power-electronic converter based device capable of protecting sensitive loads from all supply-side disturbances [5]. DVR can be assumed as an external voltage source with controllable amplitude, frequency and phase connected in series with distribution feeder, through a coupling transformer. Conventional DVR uses bulky and costly electrolytic capacitors at dc-link. This results increase in systems size, weight, cost and losses and also large input and output filters are necessary for harmonic reduction. In these DVRs, one-directional power transfer has to be carried out only. To overcome the disadvantages of traditional DVR a new ac/ac converter (Matrix Converter) based DVR is introduced to compensate both voltage sag and swell [9].

This converter has the ability of ac-ac conversion with no dc link to eliminate the energy storing element. The system is mainly composed of a source, injection transformer, bypass switch, low pass filter, matrix converter and an output load. During normal operating condition, the bypass switch is in closed position and input voltage is transferred to the load. When any abnormal condition arises, matrix converter switches are turned on and provide required compensating voltage at the output. At this time the bypass switch is in off position. The output of the converter is filtered and it is injected in series with the line through a transformer. This injected voltage is added up with the sag voltage and full output is obtained at the load.

Fig. 7.Schematic diagram of DVR with matrix converter [5].

In equation (1) L, G and inj subscripts are the load, grid, and injected quantities respectively. Also, subscript k refers to the number of phases and its value is 1, 2 and 3. During voltage swell condition, a negative voltage is injected to the line. A Least Mean Square Error method [7], [10], is used to control the switching operation of matrix converter. It can compensate voltage sag, swell and flicker, because it uses bidirectional switches. There are two possible configuration ways of building the bi-directional switch; one consisting of a transistor embedded in a diode bridge arrangement while the alternative configuration consists of two anti paralleled transistors and anti-parallel diodes. The later configuration can be implemented as either a Common Emitter (CE) or a Common Collector (CC). Here Common Emitter arrangement of switch is used [11].

V.DVR CONTROLLER DESIGN

Page 1167 during the positive half cycle of the grid voltage,

switches S1a and S2a are enable and switch S4a is driven by SPWM. During negative half cycle, S1b, S2b are ON, while S4b are driven by SPWM. The output from the SPMC is based from the switching pulse of the IGBT and will be fed to the injecting transformer and thus will compensate the voltage drop at the load side.

Fig.8. Basic Single Phase Matrix Converter.

Fig.9 SPWM Signal Generations

Table 1 Switching Operation

VI. MATLAB/SIMULINK RESULTS

Here simulation is carried out in several cases, in that 1) Compensation of Voltage Sag for Proposed Single Phase Matrix Converter Based DVR, 2). Compensation of Voltage Swell for Proposed Single Phase Matrix Converter Based DVR.

Case 1: Compensation of Voltage Sag for Proposed Single Phase Matrix Converter Based DVR

(a) With DVR

Fig.10 Matlab/Simulink Model of Proposed Single Phase Matrix Converter Based DVR for Voltage Sag

Compensation.

Fig.10 shows the Matlab/Simulink Model of Proposed Single Phase Matrix Converter Based DVR for Voltage Sag Compensation using Matlab/Simulink platform.

Page 1168 Fig.12 Source Side & Load Side Voltages

Fig.12 shows the Source Side & Load Side Voltages of Proposed Single Phase Matrix Converter Based DVR for Voltage Swell Compensation.

Fig.13 shows the THD analysis of voltage sag condition.

Case 2: Compensation of Voltage Multi sag for Proposed Single Phase Matrix Converter

Fig.15 Source Side & Load Side Voltages Fig.15 shows the Source Side & Load Side Voltages of Proposed Single Phase Matrix Converter Based DVR for Voltage Multi Sag Compensation.

VII.CONCLUSION

The proposed system provides output voltage which can be bucked/boosted and in-phase/out of phase with the supply voltage. Sinusoidal pulse width modulation technique has been used to generate the gate pulse for the bidirectional switches. The DVR is simulated using Matlab/Simulink. The simulation results show that the proposed DVR compensates voltage sag/ voltage swell quickly and provides efficient voltage regulation. A modeling and simulation was done using MATLAB/Simulink to observe the SPMC capability to operate as an AC-AC converter in the DVR system. The matrix converter used Sinusoidal Pulse Width Modulation (SPWM) as the switching technique and a PID to synthesis the output signal. PID is installed to reduce the harmonic distortion and thus attain a better result. Based from the simulation result achieved, it is proven that the SPMC is capable in producing the desired output voltage via injecting transformer to the load.

REFERENCES

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